The present invention relates to a semiconductor integrated circuit device and a technique of fabricating a semiconductor integrated circuit device, and more particularly to measures for preventing corrosion of an upper-layer wiring when a TiN film is formed inside a through-hole for connecting upper- and lower-layer wiring formed over a semiconductor substrate and over an upper electrode of a capacitor insulating film, by a chemical vapor deposition method using a metal source containing a halogen element.
When the aspect ratio of a through-hole (depth/diameter of the through-hole) for connecting upper- and lower-layer wirings formed on a semiconductor substrate is increased as an LSI is further refined and more densely integrated, it is difficult to deposit a conductive film for wiring in the through-hole. Therefore, an art for embedding a plug in a through-hole having a high aspect ratio in a plug has been used so far.
As described in Japanese Patent Laid-Open No. 204144/1996, to prevent reaction between a metal wiring layer in a microminiaturized contact hole and an underlying layer, a titanium nitride (TiN) film is used as a reaction barrier layer.
The titanium nitride film, when deposited by a CVD (Chemical Vapor Deposition) method, has a good coverage and is thus widely used as a plug material buried in a through-hole with a high aspect ratio. For example, Japanese Patent Laid-Open No. 45770/1997 discloses a technique whereby a TiN film is formed by a CVD method inside a through-hole formed in an interlayer insulating film and a tungsten film or a tungsten compound is formed over the TiN film.
A technique has been developed which deposits a TiN film as an upper electrode by a CVD method over a tantalum oxide film which is a capacitive insulating film of a capacitor. For example, Japanese Patent Laid-Open No. 219501/1997 discloses a technique for forming a TiN film as an upper electrode over a tantalum oxide film as a capacitor insulating film by a CVD method.
To deposit a TiN film by the CVD method, a source gas containing a halogen element such as titanium tetrachloride (TiCl4) is generally used. This is because a TiN film formed by using the source gas has a large step coverage and moreover, the film can be formed at a low temperature of approx. 450xc2x0 C. and thereby, there is an advantage that the characteristic of a device is not deteriorated.
However, because a TiN film formed by using a source gas containing a halogen element contains a halogen element such as chlorine produced due to decomposition of the source gas, there is a problem that the Al (aluminum) wiring formed on a through-hole in which a CVD-TiN film is embedded would be corroded because the halogen element reacts with Al. In a method of forming a tungsten film or tungsten compound film over a titanium nitride film buried in a through-hole, as described in Japanese Patent Laid-Open No. 45770/1997, although the tungsten film has a greater capability to trap halogen elements than a tungsten compound film such as a tungsten nitride film, the overall effect of trapping halogen elements by the tungsten film is small, allowing halogen elements to enter the aluminum wiring layer formed over the tungsten film, and resulting in the halogen elements corroding the aluminum. Further, the tungsten film has a poor adhesion to the underlying film and is easily peeled.
An object of the present invention is to provide a method of preventing corrosion of an Al wiring formed over a through-hole in which a CVD-TiN film is buried or a technique of preventing corrosion of an Al wiring formed over the CVD-TiN film as an upper electrode of a capacitor insulating film.
The outline of the present invention is briefly described below.
Between the titanium nitride film formed by using a gas containing halogen as a source gas and a second conductive film is provided a film which contains metal atoms that tend to bond to halogen elements and which has a higher capability to trap halogen elements than tungsten. The provision between the titanium nitride film and the second conductive film of a film that traps halogen elementsxe2x80x94which corrode the second conductive film such as an aluminum filmxe2x80x94can prevent the diffusion of the halogen elements into the second conductive film and therefore the corrosion of the second conductive film.
The trap film that contains metal atoms tending to bond to halogen elements and has a higher capability to trap halogen than tungsten may be a titanium film, a titanium nitride film, a tantalum film or a tantalum nitride film, all these formed by the sputtering method, and a titanium film, a titanium nitride film, a tantalum film or a tantalum nitride film, all these formed by the CVD method using a source gas not containing halogen as constitutional elements. Any of these films may be used as a single layer and also as a multilayer film two or more layers of these films. When used as a single layer, the titanium film formed by the sputtering method has the greatest capability to trap halogen elements. When a multilayer film comprising a titanium film formed by sputtering and a titanium nitride film formed by sputtering is used, because the titanium film has a higher trapping capability, a greater corrosion prevention effect can be produced if the titanium film is made thicker than the titanium nitride film. These trap films are preferably formed to a thickness of more than 5 nm, more preferably 20 nm or more, either as a single layer film or as a multilayer film. A thickness in excess of 120 nm results in increased resistance and is practically not preferable. The provision of such a trapping layer improves the adhesion between the titanium nitride film containing a halogen element and the interlayer insulating film.
The trap film is a film containing atoms with a halogen bonding energy in excess of 111 kcal/mol. The greater the bonding energy, the greater the capability to trap halogen. In practice it is necessary for the bonding energy to be 111 kcal/mol or higher.
The effect to prevent corrosion of this trap film when the trap film is provided immediately below the second conductive film is equivalent to the effect when one or more additional layers are provided between the second conductive film and the trap film.
The trap film such as a titanium film exhibits an excellent capability to trap halogen even when a gas containing, fluorine, bromine or iodine, not to mention chlorine, as a constitutional element is used for a source gas for the titanium nitride film. Among examples of the source gas containing halogen are titanium tetrachloride and titanium tetraiodide. Titanium tetrachloride exhibits the highest corrosiveness for metals, particularly when it is used as a source gas, and there is a definite reason to provide a trap film.
The second conductive film is a film that may be corroded and which is made of aluminum, aluminum alloy, copper or copper alloy.
The trap film is formed over the opening after the titanium nitride film containing a halogen element has been formed by the CVD method in the opening of the insulating film. In more detail, the first conductive film including a titanium nitride film formed by the CVD method using a source gas containing halogen is deposited over the insulating film on the substrate through the opening in the insulating film. After this, the first conductive film over this insulating film is removed to form a plug inside the opening and a second conductive film including as a lowermost layer a second titanium nitride film formed by the sputtering method is deposited over the insulating film including the plug surface. This second conductive film is patterned to form a wiring layer. The first conductive layer may be a multilayer film of a titanium nitride film and a tungsten film formed by the CVD method or a single layer film of a titanium nitride film formed by the CVD method. Alternatively, the first conductive film including a titanium nitride film formed by the CVD method using a source gas containing halogen as a constitutional element is deposited over the insulating film through the opening in the insulating film on the substrate where a MISFET and a capacitor is formed. After this, the first conductive film over this insulating film is removed to form a plug inside the opening and a second conductive film including as a lowermost layer a second titanium nitride film formed by the sputtering method is deposited over the insulating film including the plug surface. This second conductive film is patterned to form a wiring layer. In this case, too, the first conductive layer may be a multilayer film of a titanium nitride film and a tungsten film formed by the CVD method or a single layer of a titanium nitride film formed by the CVD method.
In the semiconductor device using a copper wiring layer, which is corroded particularly easily, the copper corrosion can be mitigated by providing a trap film such as of tantalum or tantalum nitride between the titanium nitride film containing a halogen element and the copper wiring layer.
When the titanium nitride film formed by the CVD method is used for one of the electrodes of the capacitor, the trap film such as a titanium film made by sputtering is formed over this titanium nitride film. Conventionally, polysilicon has primarily been used for the electrodes of capacitors. Polysilicon films must be formed at a high temperature of about 650xc2x0 C. The film making temperature can be reduced by the use a titanium nitride film formed by a CVD method using a source gas containing halogen as a constitutional element. The film making temperature of the titanium nitride film by the CVD method is 400xc2x0 C. to 600xc2x0 C. The relation between chlorine concentration in the titanium nitride film and the film making temperature when titanium tetrachloride is used as a source gas is shown in FIG. 46. As shown in this graph, lower film making temperature results in higher chlorine concentration in the titanium nitride film. Particularly when the film is made at temperatures below 500xc2x0 C., the extent to which the wiring layer around the storing capacitor is corroded increases. Thus, the effect to prevent corrosion of the wiring layer becomes great if the trap film of this invention is provided particularly when the titanium nitride film is formed at temperatures below 500xc2x0 C. Not only when a titanium nitride film containing halogen is formed as the storage electrode but also when a titanium nitride film is formed after an aluminum wiring layer has been formed, it is preferable that the film making temperature be below 500xc2x0 C. Forming the film at low temperatures increases the content of halogen in the titanium nitride film.
The corrosion of the conductive film can also be prevented by forming a titanium nitride film using a source gas containing halogen as a constitutional element and then annealing it in an inert gas such as nitrogen gas or rare gas. That is, annealing can remove halogen from the titanium nitride film. The annealing is performed at a temperature of 400xc2x0 C. to 800xc2x0 C., preferably at a temperature higher than that of the process in which a TiN film is formed by the CVD method. If annealing is done in the same apparatus as the film making apparatus without exposing the titanium nitride film to the atmosphere immediately after the titanium nitride film is formed, the oxidation of the surface of the titanium nitride film can be prevented. The cleaning process may be omitted. If the cleaning process is performed, it may be done either before or after the annealing, preferably after annealing. The use of warm water at 40xc2x0 C. or higher during cleaning is most effective in removing chlorine.
If water enters the titanium nitride film during a certain processing, chlorine becomes more freely movable in the device and thus the amount of chlorine moving toward the wiring layer increases, rendering the wiring layer more likely to be corroded. It is considered that the reason is because chlorine in the titanium nitride film, when contacting water, is ionized and become more freely movable seeking species to bond to. To prevent ingress of water into the titanium nitride film, the titanium nitride film is formed by using a source gas containing halogen as a constitutional element, followed by the forming of a high-density plasma CVD insulating film that has a high water blocking effect. The refractive index of the insulating film is above 1.46, and the insulating film includes Si rich. The processes during which water can enter the film include the cleaning process after dry etching and the inorganic spin-on-glass (SOG) film forming process. The inorganic SOG film forming process involves applying an inorganic SOG film and then performing a steam-baking whereby the film is baked in water steam. Thus, by forming a high-density plasma CVD insulating film under the inorganic SOG film, the corrosion of the wiring layer can be reduced. An organic SOG film may be formed instead of the high-density plasma CVD film because the organic SOG film also has a water blocking capability, though not as high as that of the high-density plasma CVD insulating film.